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City birds do it differently

BRENDAN TREMBATH: Do city birds develop different accents to their country cousins? A study by a group of researchers at Melbourne University has found that like us humans, it seems that birds do too.

And evidence suggests that this isn't just a curiosity but an adaptation to noisier urban environments that tells us something about the impact of noise on bird behaviours.

Peter Greste has been speaking to the scientists to find out more.

(Sound of birds chirping)

PETER GRESTE: Meet Zosterops lateralis - that's Silvereyes to the unscientific among us. Or more accurately, meet country Silvereyes.

Now listen to their city relatives. They aren't a different species - at least not yet - but the Melbourne University researchers have compared the two calls and discovered that they are quite different.

KIRSTEN PARRIS: We found that the birds in the cities were changing their songs in two ways.

PETER GRESTE: Dr Kirsten Parris is a senior research fellow at the School of Botany.

KIRSTEN PARRIS: Firstly they were singing at a higher pitch to move their song further away from the low frequency traffic noise and secondly the birds were singing more slowly.

PETER GRESTE: So a little like the way you'd talk if you were trying to shout above a noisy engine for example?

KIRSTEN PARRIS: That's right, so if you're in a noisy environment and you're trying to be heard, you'd generally speak more clearly and slowly and that's what the city birds are doing as well.

PETER GRESTE: There are two possible explanations for this. The first is that it is an evolutionary shift - birds with slower, higher-pitched voices are more successful at finding mates and so are better breeders. The other is that the birds shift their own voices to suit the environment - what the researchers call "plasticity".

PETER GRESTE: Do you have a sense about which it might be?

KIRSTEN PARRIS: I think probably the plastic response has better support from other studies around the world, so I think it's likely that that's the main thing that's happening with the Silvereye song.

PETER GRESTE: Now you might not think that's much of a problem, except that it's forcing the birds to use mating calls that instinctively aren't as attractive to one another. In other words, city birds will struggle more to find a mate.

And while it isn't a serious issue for species as common as the Silvereye, Dr Parris and the lead scientist Dominique Potvin believe it could be a major headache for other, rarer and more sensitive birds. Dr Parris says it's a problem that grows with every new suburb.

KIRSTEN PARRIS: If noise levels get to a certain point that birds of a particular species can't cope with then they're basically lost from those habitats. And as we build more and more roads and bigger cities and make more urban noise, the area of Australia that's covered by this noise is getting larger and larger.

PETER GRESTE: So if we're not careful to manage noise levels this may be as close as those of us in the city can get to the birdsong we take for granted.

KIRSTEN PARRIS: Cheep, cheep, cheep, cheep. How's that?

PETER GRESTE: (Laughs) That's fantastic and is that an urban one or a rural one?